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March 2002 Off-Post Quarterly Groundwater Monitoring Report
Section 4 - Quarterly Monitoring Analytical Results
All concentrations of VOCs detected in samples collected from January through March 2002 are presented in Table 4.1. Full analytical results from January through March 2002 are presented in Appendix B. PCE, TCE, and cis-1,2-DCE concentrations are displayed for each well in Figure 4.1, Figure 4.2, and Figure 4.3, respectively, to show the lateral extent of migration of these contaminants off-post. Detections of 1,2-DCA reported in the March 2002 results are likely the result of laboratory contamination. Detections of 1,2-DCA occurred in nine samples and two trip blanks. Further investigation into the source for the low-level detections of 1,2-DCA will be conducted. At this time, 1,2-DCA is not considered a constituent of concern at CSSA and the detections occurred due to laboratory method contamination. Methylene chloride continued to be detected at levels below the RL in the March 2002 event. Methylene chloride is present due to laboratory method contamination. Methylene chloride was detected in sixteen samples and three method blanks. Results from groundwater sampling are presented below. The wells are grouped by community or neighborhood for discussion of the March 2002 results. Also included in Table 4-1 are samples collected after the December 2001 event and prior to the March 2002 quarterly monitoring event.
Fifteen wells were impacted by VOCs in March 2002, three wells required new GAC systems and four GAC systems were already installed. Based on currently available data, the lateral extent of VOC contamination extends approximately 0.5 miles beyond the south and west boundaries of CSSA. The vertical extent of migration cannot be determined based on data (i.e. well completion depths) available for wells being sampled. Information providing depth of wells, pump depth, and other pertinent data to properly characterize the vertical extent of migration is not readily available.
One well in the Dominion area (DOM-2) has been sampled for two events, September 2001 and March 2002. No VOCs were detected above the RL in either of the events. No PCE or TCE has been detected in DOM-2.
Concentrations of 1,2 DCA (0.11 mg/L) and methylene chloride (0.43 mg/L) were detected at levels above the RL but below the MDL for the first time in March 2002. Methylene chloride, a common lab contaminant, was also present in the analysis method blank, indicating the likelihood this analyte was introduced as a laboratory contaminant and is not present in the groundwater. There are no known historical uses of methylene chloride on-post.
Three wells were sampled in the Fair Oaks area. FO-8 and FO-17 were sampled for the first time in March 2002. FO-J1 has been sampled for three consecutive events, from September 2001 through March 2002. FO-J1 had a detected concentration of PCE (0.25 mg/L) and TCE (0.14 �g/L) for the first time in the March 2002 event. FO-J1 had a detected concentration of cis-1,2-DCE (0.30 mg/L) in December 2001.
FO-8 and FO-17 had detected concentrations of methylene chloride (0.20 mg/L and 0.31 mg/L). FO-J1 had detected concentrations of 1,2 DCA (0.14 mg/L) and methylene chloride (0.27 mg/L). Methylene chloride was detected in FO-J1 for the second consecutive event. Methylene chloride, a common lab contaminant, was also present in the analysis method blank, indicating the likelihood that this analyte was introduced as a laboratory contaminant and is not present in the groundwater. There are no known historical uses of methylene chloride on-post.
One well was sampled in the Hidden Springs subdivision (HS-2). This is the second consecutive sampling event for HS-2 which had a previous detection of PCE at 0.16 mg/L in December 2001.
HS-2 had a detection of PCE at 0.21 mg/L for March 2002, which was above the MDL but below the RL. This is an increase in the detected PCE concentration since the December 2001 event.
HS-2 also reported detections of 1,2 DCA (0.12 mg/L), methylene chloride (0.31 mg/L), and toluene (0.12 mg/L). All detected constituents were above the MDL but below the RL. This was the second detection of methylene chloride, but the first detection of 1,2-DCA and toluene. Methylene chloride, a common lab contaminant, was also present in the analysis method blank, indicating the likelihood that this analyte was introduced as a laboratory contaminant and is not present in the groundwater.
Three wells were sampled in the I-10 area (I10-2, I10-4 and I10-7). I10-2 was sampled for the third consecutive event due to low levels of PCE and TCE detected in the September and December 2001 monitoring events. I10-4 was sampled for the second consecutive event due to low levels of PCE detected in December 2001. I10-7 was sampled for the first time in March 2002. I10-2, I10-4 and I10-7 had no detections of PCE or TCE in March 2002.
I10-4 had detections of 1,2 DCA (0.12 mg/L) and methylene chloride (0.20 mg/L), in March 2002, the first detections for these analytes in I10-4. I10-7 had detections of toluene (0.36 mg/L) and methylene chloride (0.44 mg/L). All analytes detected were above the MDL but below the RL. Methylene chloride is not a suspected groundwater contaminant at CSSA and is considered a laboratory contaminant.
Three wells (JW-9, JW-14, and JW-26) were sampled in the Jackson Woods area west of CSSA. JW-9 has been sampled for three consecutive events, and reported low levels of cis-1,2-DCE in December 2001. JW-14 has been sampled for three consecutive events, due to low levels of PCE detected in September 2001. JW-26 was sampled for the first time in March 2002.
JW-9 had a detection of methylene chloride, at 0.37 mg/L, the first detection of methylene chloride in this well. In JW-14 detected analytes were chloroform (0.33 mg/L) and methylene chloride (0.39 mg/L). Chloroform detections were above the MDL and RL but below the MCL. Methylene chloride is considered a lab contaminant, as discussed above. JW-26 had detected analytes of 1,2 DCA (0.11 mg/L), chloroform (0.11 mg/L), and methylene chloride (0.21 mg/L). All detections (besides chloroform in JW-14) were above the MDL and below the RL.
Wells LS-1, LS-2, LS-3, LS-4, LS-5, LS-6, and LS-7 were sampled in the Leon Springs area south of CSSA. These wells are located near the east, south, and west corners of the Leon Springs Villa subdivision (Figure 1.1). Due to increasing detections of PCE and TCE in various off-post wells, additional monthly sampling events were necessary to track the progress of the detected contaminants. Wells sampled monthly between the December 2001 and March 2002 quarterly monitoring events are discussed in this section in addition to the March 2002 results.
Well LS-1 was sampled quarterly since September 2001 (three events), with detections of PCE and TCE above the MDL but below the RL in each event. For March 2002, PCE was detected at 0.30 mg/L and TCE at 0.51 mg/L. LS-1 also had a detection of 1,2 DCA at 0.13 mg/L, the first detection for this analyte. LS-1 had a chloroform detection at 0.10 mg/L, the third consecutive detection for chloroform.
LS-2 has been sampled since August 2001. Due to concentrations of PCE and TCE present in LS-2, additional sampling was performed on a monthly basis since August 2001. In January 2002, PCE was reported at the highest concentration to date (4.82 mg/L) for this well. This is above the MDL and RL and approaching the MCL (5.0 mg/L). The January 2002 result for TCE was 0.2 �g/L. A sample was also collected on February 13, 2002, and PCE was detected at 2.88 mg/L. March 2002 detections included PCE at 2.9 �g/L and TCE at 0.29 mg/L.
Additional analytes detected in LS-2 included chloroform at 0.07 mg/L in January 2002. In February 2002 additional analytes detected were 1,2 DCA (0.11 mg/L) and chloroform (0.11 mg/L). In March 2002 other detections included 1,2 DCA (0.12 mg/L), and chloroform (0.11 �g/L). These concentrations were below the RL and MCL for these analytes.
LS-3 has been sampled since August 2001. Due to concentrations of PCE and TCE present in LS-3, additional sampling was performed on a monthly basis since August 2001. LS-3 was sampled on January 16, 2002, and concentrations of PCE (1.37 mg/L) and TCE (0.67 mg/L) were detected. The monthly sample collected in February 2002 reported concentrations of PCE (1.3 mg/L ) and TCE (0.69 mg/L). The March 2002 event reported concentrations of PCE (1.3 mg/L) and TCE (0.63 mg/L).
Other analytes detected in LS-3 included February 2002 detections of 1,2 DCA (0.11 mg/L) and methylene chloride (0.23 mg/L), and a March 2002 detection of toluene (0.22 mg/L). All concentrations detected in LS-3 from January through March 2002 were above the MDL but below the RL and MCL.
Due to the VOC concentrations detected in LS-2 and LS-3, plans to install a GAC unit to service both wells were submitted to and approved by the TNRCC. Installation of a GAC treatment system was initiated during April 2002, to service wells LS-2 and LS-3. The GAC system installation and Post-GAC confirmation samples will be discussed in the next quarterly report.
LS-4 has been sampled for three consecutive quarterly events since September 2001. PCE was reported in December 2001 at 0.23 �g/L and in March 2002 at 0.17 mg/L. These levels are below the RL but above the MDL. 1,2 DCA was detected at a concentration of 0.12 mg/L for the first time in March 2002, which is above the MDL and below the RL.
LS-5 was sampled for four consecutive events since August 2001. PCE was detected at low levels in August and October 2001, and TCE was reported at low levels in every event. In March 2002, TCE was detected at 0.26 mg/L, but PCE was not detected. Methylene chloride (0.25 mg/L) was also reported for the first time in March 2002.
At the time of the March 2002 sampling event, GAC units had already been installed at wells LS-6 and LS-7. To determine current groundwater conditions at these wells, samples were collected at the wellhead before treatment by the GAC filters. To determine if the filters were operating properly, additional (post-GAC) samples were collected after filtration. The post-GAC sampling results are discussed in Section 5.
LS-6 pre-GAC samples have been collected since August 2001. PCE above the MCL and TCE at low levels, below the RL, was reported in August and September 2001. PCE below the MCL and TCE below the RL continued to be reported from December 2001 to March 2002. During March 2002 the LS-6 pre-GAC sample reported PCE (2.7 mg/L) and TCE (0.2 mg/L). The PCE concentration was above the MDL and RL, but below the MCL. PCE levels have decreased steadily since the December 2001 event. In March 2002, methylene chloride (0.45 mg/L) was detected for the second consecutive event.
LS-7 pre-GAC samples have been collected since December 1999. PCE and TCE below the MCL were detected consistently since December 1999. In March 2002 the LS-7 pre-GAC sample reported concentrations of PCE (2.7 mg/L) and TCE (0.24 mg/L). As shown by the concentration trends presented in Figure 2.1, PCE reported in March 2002 began to increase compared to the recent trend of decreasing concentrations in previous sampling events. PCE and TCE concentrations have fluctuated over time in LS-7 with a minor increasing trend. Other analytes detected in the March 2002 event were naphthalene (0.12 mg/L), chloroform (0.13 mg/L), and methylene chloride (0.51 mg/L). This was the first detection for naphthalene and the second detection of methylene chloride. Inconsistent detections of chloroform have occurred since December 1999.
Three wells located on Old Fredericksburg Road were sampled (OFR-1, OFR-2, and OFR-3). OFR-1 has been sampled since December 2001 for two consecutive events. In March 2002 OFR‑1 had detected concentrations of PCE (0.42 mg/L), the same concentration reported in December 2001. Other analytes detected in March 2002 were 1,2 DCA (0.12 mg/L), toluene (0.12 mg/L), and methylene chloride (0.32 mg/L). This was the second detection of methylene chloride, but the first detections for 1,2-DCA and toluene. Detections for 1,2-DCA, toluene, and methylene chloride in March 2002 are below the RL.
OFR-2 was sampled in March 2002 for the first time since December 1995. The March 2002 event reported a detection of PCE (0.29 mg/L). 1,2-DCA was detected at 0.13 mg/L for the first time in OFR-2 in March 2002. The detections of PCE and 1,2-DCA are below the RL for these analytes.
OFR-3 has been sampled on a monthly basis since December 2001 due to a concentration of 4.2 �g/L PCE reported in October 2001. On January 16, 2002, PCE was detected at a concentration of 2.66 mg/L and TCE at 2.08 mg/L. In February 2002, PCE and TCE were again detected at levels of 3.4 mg/L and 2.58 mg/L, respectively. Concentrations of PCE and TCE were above the MDL and RL and approaching the MCL (5.0 mg/L). In March 2002 OFR-3 had reported levels of PCE (12.15 mg/L), TCE (5.65 mg/L), and cis 1,2 DCE (0.14 mg/L). PCE and TCE exceeded the MCLs (5.0 mg/L) in March 2002, and a GAC unit was installed in April 2002. Additional information on the OFR-3 GAC system installed in April 2002 and the confirmation samples collected will be submitted in the next quarterly report.
Other analytes detected over time in OFR-3 include a January 2002 detection of dichlorodifluoromethane at 0.28 mg/L. In February 2002, dichlorodifluoromethane and methylene chloride were reported at 1.43 mg/L, and 0.96 mg/L respectively. During the March 2002 monitoring event, dichlorodifluoromethane (1.48 mg/L) and methylene chloride (0.37 mg/L) were again detected.
Three wells (RFR-10, RFR-11 and RFR-12) were sampled in the Ralph Fair Road area west of CSSA.
On October 9, 2001, two GAC treatment systems were installed at well RFR-10, due to the September 2001 sampling results. RFR-10 has one GAC unit dedicated to the existing residence and the second GAC unit installed for a mobile home. To determine current groundwater conditions, water samples are collected at the wellhead before entering treatment by the GAC units. To determine if the filters were operating properly, additional (post-GAC) samples are collected after filtration through each GAC unit. The post-GAC sampling results are presented in Section 5, below.
RFR-10 pre-GAC samples have been collected since September 2001, for three consecutive events. During the March 2002 monitoring event, RFR-10 exceeded the MDL for both PCE and TCE at levels of 4.5 and 2.2 mg/L, respectively. A detected concentration of cis-1,2 DCE (0.87 �g/L) was above the MDL, but below the RL. 1,2 DCA was detected above the MDL, but below the RL, at 0.13 mg/L in March 2002. Concentrations of PCE peaked in October 2001 at a concentration of 20.89 mg/L and have decreased at each event since October 2001.
On October 16, 2001, a GAC treatment system was installed at well RFR-11, due to the September 2001 sampling results. The post-GAC sampling results are presented in Section 5, below. RFR-11 has been sampled since October 2001, for three consecutive events. The March 2002 monitoring event reported concentrations of PCE (5.71 mg/L) and TCE (1.05 mg/L). The analyte methylene chloride (0.24 mg/L) was also reported in March 2002. Methylene chloride is attributed to laboratory contamination due to the presence of methylene chloride in the associated method blank. The PCE concentration in RFR-11 shows a decreasing concentration trend since the peak reported concentration of 16.73 �g/L in October 2001.
RFR-12 was sampled during the March 2002 monitoring event. TCE was the only detected analyte at a concentration of 0.15 mg/L. This concentration is an estimation because it was detected above the MDL and below the RL. TCE concentrations have remained consistently below the RL since August 2001 in this well.